Standing-wave radio frequency exciter

ABSTRACT

A system for magnetic detection includes a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, an optical light source, an optical detector, and a radio frequency (RF) excitation source. The optical light source is configured to provide optical excitation to the magneto-optical defect center material. The optical detector is configured to receive an optical signal emitted by the magneto-optical defect center material. The RF excitation source is configured to provide RF excitation to the magneto-optical defect center material. The RF excitation source includes an RF feed connector, and a metallic material coated on the magneto-optical defect center material and electrically connected to the RF feed connecter.

FIELD

The present disclosure generally relates to magnetic detection systems, and more particularly, to a magnetic detection system with a highly efficient RF excitation.

BACKGROUND

Many advanced magnetic detection (such as imaging) systems can operate in limited conditions, for example, high vacuum and/or cryogenic temperatures, which can make them inapplicable for applications that require ambient conditions. Small size, weight and power (SWAP) magnetic sensors of moderate sensitivity, vector accuracy, and bandwidth are likewise deficient for certain detection (such as imaging) applications.

SUMMARY

According to some embodiments, there is a system for magnetic detection. The system comprises: a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, a radio frequency (RF) exciter system configured to provide RF excitation to the magneto-optical defect center material; an optical light source configured to direct excitation light to the magneto-optical defect center material; an optical detector configured to receive an optical signal emitted by the magneto-optical defect center material based on the excitation light and the RF excitation; and wherein the RF exciter system comprises: a RF source; a controller configured to control the RF source, the RF input; a RF ground; a microstrip line electrically connected to the RF input and short circuited to the RF ground adjacent the magneto-optical defect center material, wherein controller is configured to control the RF source such that a standing wave RF field is created in the magneto-optical defect center material.

According to some embodiments, the microstrip line comprises conductive traces comprising a first trace having a first width and a first length, and a second trace contacting the first trace, the second trace having a second width and a second length different from the first width and the first length.

According to some embodiments, the second trace has an impedance of less than 10Ω.

According to some embodiments, the impedance of the first trace matches a system impedance.

According to some embodiments, the first trace has an impedance of about 50Ω.

According to some embodiments, the microstrip line comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and is short circuited to the RF ground adjacent the magneto-optical defect center material.

According to some embodiments, the microstrip line further comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and short circuited to the RF ground adjacent the magneto-optical defect center material.

According to some embodiments, the microstrip line has a wavelength of about a quarter wavelength of an RF carrier frequency.

According to some embodiments, there is radio frequency (RF) exciter system for providing RF excitation to a magneto-optical defect center material comprising a plurality of magneto-optical defect centers. The RF exciter system comprises: a RF input; a controller configured to control an RF source to apply a RF signal to the RF input; a RF ground; and a microstrip line electrically connected to the RF input and short circuited to the RF ground adjacent a magneto-optical defect center material; wherein the controller is configured to control the RF source to apply an RF signal to the RF input such that a standing wave RF field is created in the magneto-optical defect center material.

According to some embodiments, the microstrip line comprises conductive traces comprising a first trace having a first width and a first length, and a second trace contacting the first trace, the second trace having a second width and a second length different from the first width and the first length.

According to some embodiments, the microstrip line comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and is short circuited to the RF ground adjacent the magneto-optical defect center material.

According to some embodiments, the microstrip line has a wavelength of about a quarter wavelength of an RF carrier frequency.

According to some embodiments, there is a radio frequency (RF) exciter system. The system comprises: a RF exciter circuit for providing RF excitation to a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, the RF exciter circuit comprising: a RF input; a RF ground; and a microstrip line electrically connected to the RF input and short circuited to the ground adjacent a magneto-optical defect center material; a controller configured to control an RF source to apply an RF signal to the RF input; wherein the controller is configured to control the RF source to apply an RF signal to the RF input such that a standing wave RF field is created in the magneto-optical defect center material; and a RF termination component configured to reduce back reflection of a RF signal from the short circuit.

According to some embodiments, the RF termination component comprises one of a non-reciprocal isolator device, or a balanced amplifier configuration.

According to some embodiments, the microstrip line comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and is short circuited to the RF ground adjacent the magneto-optical defect center material.

According to some embodiments, the microstrip line has a wavelength of about a quarter wavelength of an RF carrier frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one orientation of an Nitrogen-Vacancy (NV) center in a diamond lattice.

FIG. 2 illustrates an energy level diagram showing energy levels of spin states for the NV center.

FIG. 3 is a schematic diagram illustrating a NV center magnetic sensor system.

FIG. 4 is a graph illustrating the fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field, and also for a non-zero magnetic field having a component along the NV axis.

FIG. 5A is a schematic illustrating a Ramsey sequence of optical excitation pulses and RF excitation pulses.

FIG. 5B is a graph illustrating the fluorescence as a function of an applied RF frequency for four different NV center orientations for a non-zero magnetic field.

FIG. 6 is a schematic diagram illustrating some embodiments of a magnetic field detection system.

FIG. 7A is a schematic diagram illustrating some embodiments of a portion of a magnetic field detection system.

FIG. 7B is a schematic diagram illustrating some embodiments of a portion of a magnetic field detection system with a different arrangement of the light sources than in FIG. 7A.

FIG. 8 illustrates some embodiments of an RF excitation source of a magnetic field detection system.

FIG. 9 illustrates some embodiments of an RF excitation source oriented on its side.

FIG. 10 illustrates some embodiments of a circuit board of an RF excitation source.

FIG. 11A illustrates some embodiments of a diamond material coated with a metallic material from a top perspective view.

FIG. 11B illustrates some embodiments of a diamond material coated with a metallic material from a bottom perspective view.

FIG. 12 illustrates some embodiments of a standing-wave RF exciter system.

FIG. 13A illustrates some embodiments of a circuit diagram of a RF exciter system.

FIG. 13B illustrates some embodiments of a circuit diagram of another RF exciter system.

FIG. 14A is a graph illustrating an applied RF field as a function of frequency for a prior exciter.

FIG. 14B is a graph illustrating an applied RF field as a function of frequency for some embodiments of an exciter.

DETAILED DESCRIPTION

Some embodiments of an RF excitation source are described with respect to a diamond material with NV centers, or other magneto-optical defect center material. A metallic material as part of the RF excitation source is coated on the diamond material. The metallic material may function to provide an RF excitation to the diamond material with NV centers. A highly efficient RF excitation to the diamond material is realized.

The RF excitation source may include, in some embodiments, a block portion with a support portion supporting the diamond or other defect material. The block portion may include a first and second wall portion adjacent the support portion. The face of the second wall portion is slanted with respect to the first wall portion, and thus the second wall portion makes an angle with respect to the first wall portion, The slanted second wall portion allows both the light emitted by a readout optical light source and the light emitted by a reset optical light source to be directed to the diamond or other defect material over a variety of arrangements of the optical light sources. The slanted second wall portion allows the readout optical light source and the reset optical light source to be positioned relatively close to each other, while directing light to the same portion of the diamond or other defect material over a variety of arrangements of the optical light sources.

The intensity of the RF field applied to the diamond material by the RF excitation source will depend on the power of the system circuit. Specifically, the power is proportional to the square of the intensity of the RF field applied. It is desirable to reduce the power of the system circuit while maintaining the RF field.

The RF exciter with a short circuited microstrip line with a standing wave applied field at the diamond described herein, provides a number of advantages. The field intensity applied to the diamond for a given incident RF power is maximized. The RF exciter provides both a small field gradient and a flat frequency response. Further setting the microstrip line of the RF exciter to have a length of about a quarter wavelength produces maximum current, and thus maximum applied field.

The NV Center, Its Electronic Structure, and Optical and RF Interaction

The NV center in a diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in FIG. 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice.

The NV center may exist in a neutral charge state or a negative charge state. The neutral charge state uses the nomenclature NV⁰, while the negative charge state uses the nomenclature NV, which is adopted in this description.

The NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

The NV center has rotational symmetry, and as shown in FIG. 2, has a ground state, which is a spin triplet with ³A₂ symmetry with one spin state m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. In the absence of an external magnetic field, the m_(s)=±1 energy levels are offset from the m_(s)=0 due to spin-spin interactions, and the m_(s)=±1 energy levels are degenerate, i.e., they have the same energy. The m_(s)=0 spin state energy level is split from the m_(s)=±1 energy levels by an energy of approximately 2.87 GHz for a zero external magnetic field.

Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m_(s)=±1 energy levels, splitting the energy levels m_(s)=±1 by an amount 2 gμ_(B)Bz, where g is the g-factor, μ_(B) is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter and will not affect the computational and logic steps in the systems and methods described below.

The NV center electronic structure further includes an excited triplet state ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. The optical transitions between the ground state ³A₂ and the excited triplet ³E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet ³E and the ground state ³A₂, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

There is, however, an alternative non-radiative decay route from the triplet ³E to the ground state ³A₂ via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the m_(s)=±1 spin states of the excited triplet ³E to the intermediate energy levels is significantly greater than the transition rate from the m_(s)=0 spin state of the excited triplet ³E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet ³A₂ predominantly decays to the m_(s)=0 spin state over the m_(s)=±1 spins states. These features of the decay from the excited triplet ³E state via the intermediate singlet states A, E to the ground state triplet ³A₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m_(s)=0 spin state of the ground state ³A₂. In this way, the population of the m_(s)=0 spin state of the ground state ³A₂ may be “reset” to a maximum polarization determined by the decay rates from the triplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet ³E state is less for the m_(s)=±1 states than for the m_(s)=0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m_(s)=±1 states of the excited triplet ³E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m_(s)=±1 states increases relative to the m_(s)=0 spin, the overall fluorescence intensity will be reduced.

The NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System

FIG. 3 is a schematic diagram illustrating a NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the m_(s)=±1 states, and to measure the magnetic field based on the energy difference between the m_(s)=+1 state and the m_(s)=−1 state, as manifested by the RF frequencies corresponding to each state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source 330, which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground m_(s)=0 spin state and the m_(s)=+1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground m_(s)=0 spin state and the m_(s)=+1 spin state, reducing the population in the m_(s)=0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance and a subsequent decrease in fluorescence intensity occurs between the m_(s)=0 spin state and the m_(s)=−1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m_(s)=0 spin state and the m_(s)=−1 spin state.

The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green (light having a wavelength such that the color is green), for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the m_(s)=±1 spin states have the same energy) photon energy of approximately 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence.

The Ramsey pulse sequence is a pulsed RF-pulsed laser scheme that measures the free precession of the magnetic moment in the diamond material 320 with NV centers, and is a technique that quantum mechanically prepares and samples the electron spin state. FIG. 5A is a schematic diagram illustrating the Ramsey pulse sequence. As shown in FIG. 5A, a Ramsey pulse sequence includes optical excitation pulses and RF excitation pulses over a five-step period. In a first step, during a period 0, a first optical excitation pulse 510 is applied to the system to optically pump electrons into the ground state (i.e., m_(s)=0 spin state). This is followed by a first RF excitation pulse 520 (in the form of, for example, a microwave (MW) π/2 pulse) during a period 1. The first RF excitation pulse 520 sets the system into superposition of the m_(s)=0 and m_(s)=+1 spin states (or, alternatively, the m_(s)=0 and m_(s)=−1 spin states, depending on the choice of resonance location). During a period 2, the system is allowed to freely precess (and dephase) over a time period referred to as tau (τ). During this free precession time period, the system measures the local magnetic field and serves as a coherent integration. Next, a second RF excitation pulse 540 (in the form of, for example, a MW π/2 pulse) is applied during a period 3 to project the system back to the m_(s)=0 and m_(s)=+1 basis. Finally, during a period 4, a second optical pulse 530 is applied to optically sample the system and a measurement basis is obtained by detecting the fluorescence intensity of the system. The RF excitation pulses applied are provided at a given RF frequency, which correspond to a given NV center orientation.

In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5B illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material. Magneto-optical defect center materials include but are not limited to diamonds, Silicon Carbide (SiC) and other materials with nitrogen, boron, or other chemical defect centers. Our references to diamond-nitrogen vacancies and diamonds are applicable to magneto-optical defect materials and variations thereof.

FIG. 6 is a schematic diagram of a system 600 for a magnetic field detection system according to some embodiments.

The system 600 includes an optical light source 610, which directs optical light to an NV diamond material 620 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 630 provides RF radiation to the NV diamond material 620. The system 600 may include a magnetic field generator 670 which generates a magnetic field, which may be detected at the NV diamond material 620, or the magnetic field generator 670 may be external to the system 600. The magnetic field generator 670 may provide a biasing magnetic field.

The system 600 further includes a controller 680 arranged to receive a light detection signal from the optical detector 640 and to control the optical light source 610, the RF excitation source 630, and the magnetic field generator 670. The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system 600. The magnetic field generator 670 may be controlled by the controller 680 via an amplifier 660, for example.

The RF excitation source 630 may be controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground m_(s)=0 spin state and the m_(s)=±1 spin states as discussed above with respect to FIG. 3, or to emit RF radiation at other nonresonant photon energies.

The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical light source 610, the RF excitation source 630, and the magnetic field generator 670. The controller 680 may include a processor 682 and a memory 684, in order to control the operation of the optical light source 610, the RF excitation source 630, and the magnetic field generator 670. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical light source 610, the RF excitation source 630, and the magnetic field generator 670 to be controlled.

That is, the controller 680 may be programmed to provide control.

FIG. 7A is a schematic diagram of a portion 700 of the magnetic detection system 600 according to some embodiments. The portion 700 includes optical light source 610, the NV diamond material 620, the RF excitation source 630, and the optical detector 640 of the system 600.

Readout Optical Light Source and Reset Optical Light Source

The optical light source 610 may include a readout optical light source 710 and reset optical light source 720. The readout optical light source 710 may be a laser or a light emitting diode, for example, which emits light in the green which may be focused to the NV diamond material 620 via focusing optics 730. The readout optical light source 710 induces fluorescence in the red from the NV diamond material 620, where the fluorescence corresponds to an electronic transition of the NV electron pair from the excited state to the ground state. Referring back to FIG. 6, light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. Thus, the readout optical light source 710 induces fluorescence which is then detected by the optical detector 640, i.e., the fluorescence induced by the readout optical light source 710 is read out.

The reset optical light source 720 may provide light which is focused to the NV diamond material 620 via focusing optics 740. The reset optical light source 720 of the optical light source 610 serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization. In general, it may be desired in a reset stage to reset the spin population to the desired spin state relatively quickly to reduce the reset time, and thus to increase sensor bandwidth. In this case the reset optical light source 720 provides light of a relatively high power. Further, the reset optical light source 720 may have a lower duty cycle than readout optical light source 710, thus providing reduced heating of the system.

On the other hand, a relatively lower power may be desired for the readout optical light source 710 to provide a higher accuracy readout. The relatively lower power readout optical light source 710 beneficially allows for easier control of the spectral purity, a slower readout time with lower noise, reduced laser heating, and may be light weight and compact. Thus, the reset optical light source 720 may provide light of a higher power than that of the readout optical light source 710. The readout optical light source 710 does provide some amount of a reset function. However, a lower powered light source takes longer to provide a reset and thus is tolerable.

The readout optical light source 710 may be a laser or an LED, for example, while the reset optical light source 720 may a laser, or an LED. Exemplary arrangements are as follows. The readout optical light source 710 may be a lower powered laser, and the reset optical light source 720 may be a higher powered laser with a lower duty cycle. The readout optical light source 710 may be a lower powered laser, and the reset optical light source 720 may be a bank of LED flash-bulbs. The readout optical light source 710 may be an LED, and the reset optical light source 720 may be a bank of LED flash-bulbs.

RF Excitation Source and NV Diamond Material

FIG. 8 illustrates some embodiments of the RF excitation source 630 with the diamond material 620 with NV centers. The RF excitation source 630 includes a block portion 820, RF feed connector 830 with output 832, and circuit board 840. The RF feed connector 830 may be electronically connected to the controller 680 (see FIG. 6), such as via a cable, for example, where the controller 680 provides an RF signal whereby the controller 680 may provide an RF signal to the RF feed connector 830.

The block portion 820 may include a support portion 850, which supports the diamond material 620 with NV centers. The block portion 820 may further include a first wall portion 860 and a second wall portion 862 adjacent the support portion 850. The first wall portion 860 is on one side of the support portion 850, while the second wall portion 862 is on another side of the support portion 850 opposite to the first side. The face of the second wall portion 862 is slanted with respect to the first wall portion 860, and thus the second wall portion 862 makes an angle θ with respect to the first wall portion 860,

FIG. 7B shows some embodiments of a portion of a magnetic field detection system with a different arrangement of the light sources than in FIG. 7A. The slanted second wall portion 862 allows both the light emitted by the readout optical light source 710 and the light emitted by the reset optical light source 720 (see FIGS. 7A and 7B) to be directed at a proper angle to the diamond material 620 with NV centers over a variety of arrangements of the readout optical light source 710 and the reset optical light source 720. In particular, the slanted second wall portion 862 allows the readout optical light source 710 and the reset optical light source 720 to be positioned relatively close to each other, over a variety of arrangements of the readout optical light source 710 and the reset optical light source 720, while directing light to the same portion of the diamond material 620 with NV centers.

In the arrangement of FIG. 7A the light sources 710 and 720 direct light on one side of the first wall portion 860, while in FIG. 7B the light source 710 and 720 direct light on another side of the of the first wall portion 860. The face of the second wall portion 862 is slanted with respect to the first wall portion 860 to allow either of the arrangements of the light sources 710 and 720 in FIG. 7A or 7B to direct light to the diamond material 620 with NV centers without blocking the light.

The block portion 820 may comprise an electrically and thermally conductive material. For example, the block portion 820 may be formed of a metal such as copper or aluminum. The good thermal conductivity of the block portion 820 allows the block portion to function as a heat sink drawing heat away from the diamond material 620 with NV centers. The electrically conductive nature of the block portion 820 allows that a metallic material 870 (see FIG. 11) provided on the diamond material 620 with NV centers may electrically short with the block portion 820.

FIG. 9 illustrates the RF excitation source 630 with the diamond material 620 of FIG. 8 oriented on its side. The block portion 820 has both side holes 920 and bottom holes 930. The side holes 920 allow for mounting the block portion 820 on its side for edge injection of light into the diamond material 620. The bottom holes 930 allow for mounting the block portion 820 on its bottom for side injection of light. Other orientations for the block portion 820 are possible.

FIG. 10 illustrates a top view of the circuit board 840 of FIG. 8 in more detail with conductive traces shown. The circuit board 840 includes a notch 1010 within which the RF connector 830 is positioned. The circuit board 840 may include an insulating board 1060 with conductive traces thereon. The output 832 of the RF feed connector 830 is electrically connected to a RF connector output trace 1020, which in turn is connected to a first trace 1030, which in turn is electrically connected to a second trace 1040. The traces 1020, 1030 and 1040 may be conducting metals, for example, such as copper or aluminum.

FIG. 11A illustrates a diamond material 620 coated with a metallic material 870 from a top perspective view. FIG. 11B illustrates a diamond material 620 coated with a metallic material 870 from a bottom perspective view. The metallic material 870 may be gold, copper, silver, or aluminum, for example. The metallic material 870 has a top 870 a, bottom 870 c, and a side portion 870 b connecting the top 870 a and bottom 870 c, and is designed to electrically short to the underlying block portion 820 via the metallic material on the side portion, where the block portion 820 functions as a RF ground. The second trace 1040 (see FIG. 10) is electrically connected to the metallic material 870 on the diamond material 620 with NV centers. As mentioned above, the electrically conductive nature of the block portion 820 allows that the metallic material 870 provided on the diamond material 620 with NV centers may electrically short with the block portion 820. In this regard, the second trace 1030 is electrically connected to the metallic material 870, and the RF signal connector 830 is driven by an RF signal, where the signal propagates along the traces 1020, 1030 and 1040. The second trace 1040 may have a width corresponding to the width of the diamond material 620 with NV centers, and may be electrically connected to the metallic material 870 along the width of the second trace 1040. The second trace 1040 may be electrically connected to the metallic material 870 by a ribbon bond, for example.

Because the diamond material 620 with NV centers is coated with a metallic material 870, where the metallic material 870 functions to provide an RF excitation to the diamond material 620 with NV centers, a highly efficient RF excitation to the diamond material is possible.

Standing-Wave RF Exciter

FIG. 12 illustrates a standing-wave RF exciter system 1200 according to some embodiments. The system 1200 includes a controller 1210 and an RF exciter circuit 1220. The RF exciter circuit 1220 includes an RF feed connector 1230 with an RF feed connector output 1235, and a conducting trace including a RF connector output trace 1240, a first trace 1245 and a second trace 1250. The output 1235 of the RF feed connector 1230 is electrically connected to the RF connector output trace 1240. The RF connector output trace 1240 in turn is electrically connected to the first trace 1245, which in turn is electrically connected to second trace 1250. The first trace 1245 has an impedance which matches that of the system circuit impedance, for example, if the system circuit impedance is 50Ω, which is typical, the first trace 1245 should have an impedance of 50Ω.

The second trace 1250 has a width where the impedance of the second trace 1250 is lower than that of the first trace 1245. The second trace 1250 is electrically connected to the metallic material 870 on the diamond material 620. The metallic material 870 is formed on a top, a bottom, and a side portion connecting the metal on the top and bottom, of the diamond material 620, and is designed to electrically short to the underlying block portion 820, which functions as a RF ground.

The controller 1210 is programmed or otherwise configured to control an RF source 1270 so as to apply an RF signal to the RF feed connector output 1235. The controller 1210 may cause the RF source 1270 to apply an RF signal to the RF feed connector 1230 which is then applied to the traces 1240, 1245 and 1250, which are short-circuited to the block portion 820 via the metallic material 870 on the diamond material 620.

The controller 1210 may control the RF source 1270 so as apply an RF signal to RF feed connector 1235 such that a standing wave is produced within the diamond 630. In this regard, the controller 1210 may include or control the RF source 1270, which may comprise an external or internal oscillator circuit, for example. The signal may be a modulated sinusoidal with a RF carrier frequency, for example. The second trace 1250 has a width where the impedance of the second trace 1250 is lower relative to that of the first trace 1245. For example, if the impedance of the first trace 1245 is about 50Ω, then the impedance of the second trace 1250 may be less than 10Ω, for example. The low impedance of the second trace 1250 provides a relatively high RF field which is applied to the diamond material 620.

The second trace 1250 may have a relatively wide width, such as for example greater than 2 mm, so that the second trace 1250 has a relatively low impedance. The traces 1245 and 1250, along with the metallic material 870 on the diamond material 620, act as a microstrip line. The relatively wide second trace 1250 along with the metallic material 870 which is coated on the diamond material 620 beneficially provides for a small field gradient of the RF field applied to the diamond material 620. The good RF field uniformity is due in part to the arranged microstrip line.

The metallic material 870 on the diamond material 620 is located at the end, and is part of, the microstrip line, which also comprises the traces 1245 and 1250. The short circuiting of the metallic material 870 to the block portion 820 provides current and thus an applied field maxima at the diamond. The standing wave field which is applied results in doubling the RF field applied to the diamond material 620. This means a 4-times decrease in the power needed to maintain a particular RF field.

Thus, providing a standing wave application of the RF field to the diamond material 620 using a microstrip line short circuit at the diamond material 620 provided with the metallic material 870 covering the diamond material 620 provides a power reduction needed to maintain the RF field intensity in the diamond material 620, and a low RF field gradient in the diamond material 620.

The magnitude of the RF field applied at the diamond material 620 will also depend on the length of the microstrip line, which includes traces 1245 and 1250, along with the metallic material 870 on the diamond material 620. In an ideal case a length of the microstrip line of a quarter wavelength of the RF carrier frequency will produce the maximum current, and thus the maximum RF field applied to the diamond material 620. Incorporating the diamond to the system, however, affects the nature of the standing wave, resulting in a different optimal length than a quarter wavelength. This length can be found computationally, and is generally shorter than a quarter wavelength. Thus, the length of the microstrip lines is about a quarter wavelength and is set to provide a maximum magnitude of the RF applied field applied to the diamond material 620.

FIGS. 13A and 13B are circuit diagrams illustrating RF exciter systems including the RF exciter circuit 1220 according to some embodiments having a non-reciprocal isolation arrangement and a balanced amplifier arrangement, respectively.

Except for small ohmic and radiative losses in the exciter, all of the power incident to the microstrip line will be reflected back from the short to an RF amplifier of the system. To avoid this backreflection, the systems 1300A and 1300B in FIGS. 13A and 13B, respectively, include an RF termination component. The RF termination component may be, for example, a non-reciprocal isolator device as in FIG. 13A, or a balanced amplifier configuration as in FIG. 13B. If the non-reciprocal isolator device has magnetic materials, a balanced amplifier is preferred to avoid interference due to the magnetic fields.

FIG. 13A includes, in addition to RF exciter circuit 1220, controller 1210 and RF source 1270 of the FIG. 12 system, an amplifier 1310 and a RF isolator 1320. The RF signal from the RF source 1270 is amplified by the amplifier 1310, and the amplified signal is input to the RF isolator 1320, which provides an RF termination function, and is then output to the exciter circuit 1220.

The balanced amplifier arrangement of FIG. 13B includes, in addition to RF exciter circuit 1220, controller 1210 and RF source 1270 of the FIG. 12 system, a quadrature component 1330 arranged before two amplifiers 1340 and 1345, followed by another quadrature component 1350 arranged after the two amplifiers 1340 and 1345. The RF signal from the RF source 1270 is input to the first quadrature component 1330, and then quadrature result is input to the two amplifiers 1340 and 1345. The amplified signal from the two amplifiers 1340 and 1345 is then output to the second quadrature component 1350, and the quadrature result is input to the exciter circuit 1220.

FIGS. 14A and 14B illustrate the estimated applied field for, respectively, a prior RF exciter, and an RF exciter with a short circuited microstrip line with a standing wave applied field at the diamond. The prior RF exciter for FIG. 14A employed a 16W RF power amplifier running at saturation. The RF exciter with a short circuited microstrip line with a standing wave applied field employed a 300 mW low noise amplifier (LNA) running in the linear regime (40 mW in) to produce an equivalent applied field. FIGS. 14A and 14B illustrate the applied field both with and without a balanced amplifier in the circuit. As can be seen, for the RF exciter with a short circuited microstrip line with a standing wave applied field in FIG. 4B the applied field (Relative |H|) as a function of frequency over the frequency range of 2.6 to 3.1 GHz shows a flat frequency response in particular with an addition of a balanced amplifier. The frequency response shown in FIG. 14B is an improvement over that in FIG. 14A.

The RF exciter with a short circuited microstrip line with a standing wave applied field at the diamond described above, provides a number of advantages. The field intensity applied to the diamond for a given incident RF power is maximized. The RF exciter provides both a small field gradient and a flat frequency response. Further setting the microstrip line of the RF exciter to have a length of about a quarter wavelength produces maximum current, and thus maximum applied field.

The embodiments of the inventive concepts disclosed herein have been described in detail with particular reference to preferred embodiments thereof, but it will be understood by those skilled in the art that variations and modifications can be effected within the spirit and scope of the inventive concepts. 

What is claimed is:
 1. A system for magnetic detection, comprising: a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, a radio frequency (RF) exciter system configured to provide RF excitation to the magneto-optical defect center material; an optical light source configured to direct excitation light to the magneto-optical defect center material; an optical detector configured to receive an optical signal emitted by the magneto-optical defect center material based on the excitation light and the RF excitation; and wherein the RF exciter system comprises: a RF source; a controller configured to control the RF source, the RF input; a RF ground; a microstrip line electrically connected to the RF input and short circuited to the RF ground adjacent the magneto-optical defect center material, wherein controller is configured to control the RF source such that a standing wave RF field is created in the magneto-optical defect center material.
 2. The system of claim 1, wherein the microstrip line comprises conductive traces comprising a first trace having a first width and a first length, and a second trace contacting the first trace, the second trace having a second width and a second length different from the first width and the first length.
 3. The system of claim 2, wherein the second trace has an impedance of less than 10Ω.
 4. The system of claim 2, wherein the impedance of the first trace matches a system impedance.
 5. The system of claim 4, wherein the first trace has an impedance of about 50Ω.
 6. The system of claim 1, wherein the microstrip line comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and is short circuited to the RF ground adjacent the magneto-optical defect center material.
 7. The system of claim 2, wherein the microstrip line further comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and short circuited to the RF ground adjacent the magneto-optical defect center material.
 8. The system of claim 1, wherein the microstrip line has a wavelength of about a quarter wavelength of an RF carrier frequency.
 9. A radio frequency (RF) exciter system for providing RF excitation to a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, the RF exciter system comprising: a RF input; a controller configured to control an RF source to apply a RF signal to the RF input; a RF ground; and a microstrip line electrically connected to the RF input and short circuited to the RF ground adjacent a magneto-optical defect center material; wherein the controller is configured to control the RF source to apply an RF signal to the RF input such that a standing wave RF field is created in the magneto-optical defect center material.
 10. The RF excitation source of claim 9, wherein the microstrip line comprises conductive traces comprising a first trace having a first width and a first length, and a second trace contacting the first trace, the second trace having a second width and a second length different from the first width and the first length.
 11. The RF excitation source of claim 9, wherein the microstrip line comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and is short circuited to the RF ground adjacent the magneto-optical defect center material.
 12. The RF excitation source of claim 1, wherein the microstrip line has a wavelength of about a quarter wavelength of an RF carrier frequency.
 13. A radio frequency (RF) exciter system, comprising: a RF exciter circuit for providing RF excitation to a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, the RF exciter circuit comprising: a RF input; a RF ground; and a microstrip line electrically connected to the RF input and short circuited to the ground adjacent a magneto-optical defect center material; a controller configured to control an RF source to apply an RF signal to the RF input; wherein the controller is configured to control the RF source to apply an RF signal to the RF input such that a standing wave RF field is created in the magneto-optical defect center material; and a RF termination component configured to reduce back reflection of a RF signal from the short circuit.
 14. The circuit of claim 13, wherein the RF termination component comprises one of a non-reciprocal isolator device, or a balanced amplifier configuration.
 15. The circuit of claim 13, wherein the microstrip line comprises a metallic material coated at least over a top surface, a bottom surface, and a side surface of the magneto-optical defect center material, and is short circuited to the RF ground adjacent the magneto-optical defect center material.
 16. The circuit of claim 13, wherein the microstrip line has a wavelength of about a quarter wavelength of an RF carrier frequency. 